U.S. patent application number 11/191733 was filed with the patent office on 2006-02-02 for printed circuit board and method for producing such a printed circuit board.
This patent application is currently assigned to Patent-Treuhand-Gesellschaft fur elektrische Gluhlampen mbH. Invention is credited to Jens Florian Hockel, Patrick Muller.
Application Number | 20060023432 11/191733 |
Document ID | / |
Family ID | 35169245 |
Filed Date | 2006-02-02 |
United States Patent
Application |
20060023432 |
Kind Code |
A1 |
Hockel; Jens Florian ; et
al. |
February 2, 2006 |
Printed circuit board and method for producing such a printed
circuit board
Abstract
A printed circuit board having a thermally conductive and
electrically insulating layer (1) at the top side of the printed
circuit board (6), and a heat conducting element (2) which
thermally connects the layer (1) to the underside of the printed
circuit board (6). Furthermore, a method for producing such a
printed circuit board (6) is described.
Inventors: |
Hockel; Jens Florian;
(Munchen, DE) ; Muller; Patrick; (Karlsfeld,
DE) |
Correspondence
Address: |
COHEN, PONTANI, LIEBERMAN & PAVANE
Suite 1210
551 Fifth Avenue
New York
NY
10176
US
|
Assignee: |
Patent-Treuhand-Gesellschaft fur
elektrische Gluhlampen mbH
Munich
DE
|
Family ID: |
35169245 |
Appl. No.: |
11/191733 |
Filed: |
July 28, 2005 |
Current U.S.
Class: |
361/748 |
Current CPC
Class: |
H05K 2201/0323 20130101;
H05K 1/0204 20130101; H05K 2201/10106 20130101; H05K 2201/10416
20130101 |
Class at
Publication: |
361/748 |
International
Class: |
H05K 7/06 20060101
H05K007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 30, 2004 |
DE |
10 2004 036 960.7 |
Claims
1. A printed circuit board, comprising: a thermally conductive and
electrically insulating layer (1) at a top side of the printed
circuit board (6); and a heat conducting element (2), which
thermally connects said layer (1) to an underside of the printed
circuit board (6).
2. The printed circuit board according to claim 1, in which the
layer (1) contains at least one material having an electrical
resistivity of at least 10.sup.2 .OMEGA.m and a thermal
conductivity of at least 10.sup.2 W/mK.
3. The printed circuit board according to claim 1, in which the
layer (1) contains diamondlike carbon.
4. The printed circuit board according to claim 1, in which the
layer (1) has a thickness of between 1 .mu.m and 3 .mu.m.
5. The printed circuit board according to claim 1, in which the
heat conducting element (2) connects the layer (1) to the underside
of the printed circuit board (6) on a direct path.
6. The printed circuit board according to claim 1, in which the
layer (1) is coated on at least one part of a surface of the heat
conducting element (2).
7. The printed circuit board according to claim 1, in which the
heat conducting element (2) contains a metal.
8. The printed circuit board according to claim 1, in which the
printed circuit board (6) has a perforation in which the heat
conducting element (2) is arranged.
9. Printed circuit board according to claim 1, in which the printed
circuit board (6) contains at least one of the following materials:
copper, FR4.
10. The printed circuit board according to claim 1, in which the
underside of the printed circuit board (6) is at least partially
coated with a thermally conductive and electrically insulating
material (7).
11. The printed circuit board according to claim 10, in which the
underside coating (7) of the printed circuit board (6) contains
diamondlike carbon.
12. The printed circuit board according to claim 10, in which the
underside coating (7) of the printed circuit board (6) has a
thickness of between 1 .mu.m and 3 .mu.m.
13. An optoelectronic arrangement, comprising: a printed circuit
board (6) according to claim 1 and an optoelectronic component
(20), which is in contact with the layer at least in places.
14. The optoelectronic arrangement according to claim 13, in which
the layer (1) is coated on at least that part of the optoelectronic
component (20) which is in contact with the heat conducting element
(2).
15. The optoelectronic arrangement according to claim 13, in which
at least that part of the optoelectronic component (20) which is in
contact with the layer (1) is coated with a thermally conductive
and electrically insulating material (21).
16. The optoelectronic arrangement according to claim 15, in which
the coating (21) of the optoelectronic component (20) contains
diamondlike carbon.
17. The optoelectronic arrangement according to claim 13, in which
the optoelectronic component (20) has an electrical power
consumption of at least one watt.
18. The optoelectronic arrangement according to claim 13, in which
the optoelectronic component (20) is one of the following
components: light emitting diode, laser diode.
19. A method for producing a printed circuit board, comprising: a)
providing a printed circuit board (6); b) producing a perforation
in the printed circuit board (6); c) introducing a heat conducting
element (2) into the perforation of the printed circuit board (6);
and d) coating (7) of at least parts of an underside of the printed
circuit board (6) with diamondlike carbon.
20. Use of a body (2, 22) coated with diamondlike carbon for
dissipating the heat from an optoelectronic component.
21. Use according to claim 20, wherein the body (2, 22) comprises
copper.
Description
RELATED APPLICATIONS
[0001] This patent application claims the priority of German patent
application 10 2004 036 960.7, filed Jul. 30, 2004, the disclosure
content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a printed circuit board.
Furthermore, the invention relates to a method for producing a
printed circuit board.
BACKGROUND OF THE INVENTION
[0003] The document DE 102 349 95 A1 discloses a light emitting
diode arrangement in which a light emitting diode component is
fixed on an electrically conductive connection board. The
electrically conductive connection board comprises a carrier body,
in which is arranged an insert that conducts heat better than the
material of the carrier body.
SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a
printed circuit board having improved heat conducting
properties.
[0005] Another object of the invention to provide a method for
producing such a printed circuit board.
[0006] These and other objects are attained in accordance with one
aspect of the present invention directed to a printed circuit board
having a thermally conductive and electrically insulating layer.
The thermally conductive and electrically insulating layer is
situated, for example, at the top side of the printed circuit
board, and a heat conducting element thermally connects the layer
to the underside of the circuit board.
[0007] The printed circuit board has, for example, a basic body
containing an electrically insulating material. Patterned conductor
tracks containing an electrically conductive material are applied
to at least parts of the surface of the basic body of the printed
circuit board. By way of example, a component that is to be fixed
on the printed circuit board can be electrically contact-connected
via the conductor tracks.
[0008] The printed circuit board furthermore has a heat conducting
element. The heat conducting element connects the thermally
conductive and electrically insulating layer to the underside of
the printed circuit board.
[0009] For this purpose, there is preferably an areal contact
between the layer and at least one part of the surface of the heat
conducting element. By means of this areal contact, the layer is
thermally coupled to the heat conducting element, so that heat can
transfer from the layer--preferably by means of heat conduction--to
the heat conducting element. The heat is passed on to the underside
of the printed circuit board by the heat conducting element,
preferably once again for the most part by means of heat
conduction.
[0010] In this context, "for the most part by means of heat
conduction" means that other mechanisms of heat emission, such as
thermal radiation for example, are also possible. However, these
portions are of secondary importance and, at most, contribute a
negligibly small proportion to the heat emission.
[0011] From the heat conducting element, the heat may be emitted to
the underside of the printed circuit board and from there be
distributed areally over the underside of the printed circuit
board. However, it is also possible for the heat from the heat
conducting element to be emitted for example to a heat sink fitted
on the underside of the printed circuit board, without previously
being distributed in the area of the underside of the printed
circuit board.
[0012] In one embodiment of the printed circuit board, the
thermally conductive and electrically insulating layer contains at
least one material having an electrical resistivity of at least
10.sup.2 .OMEGA.m. The layer preferably has an electrical
resistivity of at least 10.sup.5 .OMEGA.m, particularly preferably
of at least 10.sup.9 .OMEGA.m.
[0013] The material furthermore has a thermal conductivity of at
least 100 W/mK, preferably of at least 300 W/mK, particularly
preferably of at least 600 W/mK.
[0014] In one embodiment of the printed circuit board, the material
is additionally distinguished by a hardness of at least 2 according
to Mohs' scale. The hardness is preferably at least 5, particularly
preferably at least 8. The hardness of pure diamond is 10 according
to this scale.
[0015] In a further exemplary embodiment of the printed circuit
board, the thermally conductive and electrically insulating layer
additionally has a microhardness according to Vickers of at least
500 kg/mm.sup.2, preferably of at least 1000 kg/mm.sup.2,
particularly preferably of at least 2000 kg/mm.sup.2.
[0016] The layer is furthermore preferably particularly
temperature-resistant in that it is not harmed by high
temperatures. The layer is temperature-resistant in air up to at
least 150.degree. C.; the layer is preferably temperature-resistant
up to at least 250.degree. C., particularly preferably up to at
least 350.degree. C.
[0017] The layer may also be distinguished by high corrosion
resistance. The layer is particularly preferably resistant to
salts, acids and alkaline solutions.
[0018] To summarize, the layer at least exhibits very good thermal
conduction, very good electrical insulation or is particularly
resistant mechanically, for example to scratches. The layer
preferably has at least two of the properties mentioned. The layer
is particularly preferably distinguished by the fact that it
exhibits very good thermal conduction, very good electrical
insulation and is additionally particularly resistant mechanically.
In addition, the layer is preferably particularly temperature- and
corrosion-resistant.
[0019] In one embodiment of the printed circuit board, the
thickness of the thermally conductive and electrically insulating
layer is between 1 .mu.m and 3 .mu.m. In this case, the layer
thickness is adapted, for example, to the dielectric constant of
the layer material. It is preferably chosen to be thick enough that
an electrical breakdown during operation of a component fixed on
the printed circuit board can, as far as possible, be
prevented.
[0020] For this purpose, the layer may contain diamondlike carbon,
for example. Diamondlike carbon (DLC) is distinguished by a
particularly good thermal conductivity, a high electrical
resistance and a high mechanical loading capacity. The thermal
conductivity of diamondlike carbon is up to 700 W/mK, the
electrical resistivity is approximately 10.sup.10 .OMEGA.m, the
dielectric constant is approximately 8, the Mohs' hardness of
diamondlike carbon is 9, and the Vickers hardness of a layer
containing diamondlike carbon is between 2000 and 5000
kg/mm.sup.2.
[0021] In addition to diamondlike carbon, however, layers made of
other materials such as, for example, other diamondlike materials
(diamondlike nanocomposites--DLN) are also conceivable.
[0022] In a preferred embodiment of the printed circuit board, the
heat conducting element connects the thermally conductive and
electrically insulating layer to the underside of the printed
circuit board on a direct path. That is to say that the heat
conducting element constitutes a thermal connection between the
layer and the underside of the printed circuit board in the case of
which heat entering the heat conducting element at the layer, for
example, can be passed on to the underside of the printed circuit
board on a substantially straight path. In this case,
"substantially straight" means that a part of the heat entering the
heat conducting element at the layer may be emitted laterally, for
example, to the basic body of the printed circuit board. However, a
large part of the heat is forwarded directly from the top side of
the printed circuit board to the underside of the printed circuit
board by the heat conducting element.
[0023] In a further embodiment of the printed circuit board, the
thermally conductive and electrically insulating layer is provided
by a coating of at least one part of the surface of the heat
conducting element. By way of example, that part of the surface of
the heat conducting element which is situated on the side of the
top side of the printed circuit board is coated.
[0024] The coating of the heat conducting element may be effected
for example by means of a plasma coating method such as PECVD
(Plasma Enhanced Chemical Vapor Deposition). A layer produced in
this way is distinguished particularly by its uniform thickness and
homogeneous composition.
[0025] In one embodiment of the printed circuit board, the heat
conducting element contains a semiconductor material or a metal.
The heat conducting element preferably contains copper, for
example. The heat conducting element particularly preferably
consists of copper.
[0026] In a further embodiment of the printed circuit board, the
printed circuit board has a perforation in which the heat
conducting element is arranged. The perforation may be, for
example, a hole through the printed circuit board. The heat
conducting element is, for example, plugged into the perforation.
For mechanical fixing, the heat conducting element may be
adhesively bonded to the basic body of the printed circuit board,
for example, by means of a thermally stable adhesive. However,
other types of fixing such as soldering, for example, are also
possible in order to fix the heat conducting element in the
perforation.
[0027] The printed circuit board may be a commercially available
FR4 printed circuit board coated with copper on both sides. This
has the advantage that the printed circuit board described is a
particularly cost-effective alternative to metal core printed
circuit boards (MCPCBs) which are usually used in connection with
components generating a great deal of heat.
[0028] In a further embodiment, the printed circuit board is coated
with a thermally conductive and electrically insulating material at
its underside. This underside coating preferably covers both the
underside of the basic body of the printed circuit board and the
heat conductor at least partially.
[0029] There is preferably a connection between that region of the
underside coating which covers the heat conducting element and the
region which covers the remaining underside of the printed circuit
board. In this way, it is possible to distribute the heat emitted
by the heat conductor on the underside of the printed circuit
board. The heat can then be emitted from the underside to the
surroundings over a particularly large area. By way of example, the
printed circuit board may be thermally coupled to a heat sink by
its underside, so that the heat is emitted from the underside of
the printed circuit board to the heat sink over a large area.
[0030] The underside coating particularly preferably has a
thickness of between 1 .mu.m and 3 .mu.m. Such a small thickness of
the underside coating contributes to the heat being distributed
preferably areally on the underside.
[0031] The underside coating contains diamondlike carbon, for
example. In addition to the good thermal conductivity and the high
electrical resistance, the underside coating is then additionally
also distinguished by a high mechanical resistance which affords
protection of the printed circuit board against being stratched,
for example. In this case, the underside coating is preferably
applied on the underside of the printed circuit board by means of a
plasma coating method.
[0032] In addition to diamondlike carbon, however, layers made of
other materials such as, for example, other diamondlike materials
(diamondlike nanocomposites--DLN) are also usable.
[0033] Furthermore, an optoelectronic arrangement is provided,
which has one of the above-described printed circuit boards and an
optoelectronic component.
[0034] The optoelectronic component is preferably in contact with
the thermally conductive and electrically insulating layer at least
in places in that at least some parts of the optoelectronic
component are in contact with the insulating layer. For this
purpose, the layer may be provided, for example, by an at least
partial coating of that part of the optoelectronic component which
is in contact with the heat conducting element.
[0035] By way of example, the layer is applied to an area of the
component capable of coupling-out a particularly large amount of
heat. This may involve, for example, partial regions of a thermal
connection part of the optoelectronic component that are freely
accessible from the exterior of the component. Moreover, it is also
possible for the layer to be applied directly to at least parts of
the surface of the semiconductor chip or the semiconductor chips of
the optoelectronic component or for the layer to be applied to at
least parts of a contact metallization of the semiconductor chip.
The heat generated in the chip during operation of the component
can be emitted directly to the heat conducting element in this
way.
[0036] It is also possible for the layer to be situated as a
coating on the surface of the heat conducting element and for the
optoelectronic component to be free of such a coating. At least one
part of the optoelectronic component then bears on the layer or is
fixed on the layer. The component may be fixed on the layer for
example by means of a thermally stable adhesive or by means of a
solder. In this case, it is possible for a thermal connection part
of the chip to bear at least partially on the layer. However, it is
also possible for at least parts of the semiconductor chip to bear
directly on the layer.
[0037] In a further embodiment of the optoelectronic arrangement,
it is additionally possible for at least that part of the
optoelectronic component which is in contact with the layer to be
at least partially coated with a thermally conductive and
electrically insulating material. The coating of the component and
the layer are preferably in thermal contact with one another. In
this case, the layer may be provided for example by a coating of
the surface of the heat conducting element which faces the coating
of the component. The coating of the optoelectronic component
preferably contains diamondlike carbon. Particularly preferably,
both the layer on the heat conducting element and the coating of
the optoelectronic component contain diamondlike carbon.
Particularly preferably, both layers comprise diamondlike
carbon.
[0038] In addition to diamondlike carbon, however, layers made of
other materials such as, for example, other diamondlike materials
(diamondlike nanocomposites--DLN) are also usable.
[0039] In a further embodiment of the optoelectronic arrangement,
the component has an electrical power consumption of at least 1 W.
Such components customarily generate a high heat output during
operation. Therefore, it is necessary to take measures to dissipate
the heat from the component particularly rapidly and efficiently.
The printed circuit board specified constitutes in this case a
particularly cost-effective alternative to the metal core printed
circuit boards that are usually used.
[0040] Another aspect of the invention is directed to a method for
producing a printed circuit board. For this purpose, firstly a
printed circuit board is provided. The printed circuit board may be
for example a commercially available printed circuit board (PCB),
such as, for example, an FR4 board coated with copper on both
sides.
[0041] The subsequent method step involves producing a perforation
in the printed circuit board. The perforation may be produced, for
example, by means of drilling through or stamping through the
printed circuit board.
[0042] After this method step, a heat conducting element is
introduced into the perforation. The heat conducting element is
preferably fixed in the perforation of the printed circuit board.
This can be done, for example, by means of adhesively bonding it on
using a thermally stable adhesive or by soldering on the heat
conducting element. The heat conducting element is, for example, a
copper lamina or a copper rivet. The copper lamina is preferably
coated with a thermally conductive and electrically insulating
material at least at its surface facing the top side of the printed
circuit board. This layer particularly preferably contains
diamondlike carbon.
[0043] In a further method step, the underside of the printed
circuit board may be coated with diamondlike carbon. This layer
preferably covers both the heat conducting element and the
remaining surface of the underside of the printed circuit board at
least partially. In this way, the heat conducting element can be
coupled to the remaining underside of the printed circuit board in
a manner exhibiting particularly good conduction.
[0044] The use of a body coated with diamondlike carbon for
dissipating the heat from an optoelectronic component is
furthermore described. The body may be a heat conducting element,
by way of example. The heat conducting element preferably contains
a material exhibiting good thermal conduction and is coated with
diamondlike carbon at least at one of its surfaces. However, the
body may also be the optoelectronic component, which is coated with
diamondlike carbon in places. In this case, the component is
preferably coated at areas of the component via which a
particularly large amount of heat can be emitted to the
surroundings. Thus, by way of example, a thermal connection part of
the component may be coated with diamondlike carbon. However, it is
also possible for parts of the surface of the semiconductor chip,
of the chip carrier or of a contact metallization of the chip to be
coated with diamondlike carbon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] The printed circuit board described here is explained in
more detail below with reference to exemplary embodiments and the
associated figures.
[0046] FIG. 1 shows a schematic sectional illustration of a first
exemplary embodiment of a printed circuit board described here.
[0047] FIG. 2 shows a schematic sectional illustration of a second
exemplary embodiment of a printed circuit board described here.
[0048] FIG. 3 shows an exemplary embodiment of the optoelectronic
arrangement described here.
[0049] FIG. 4 shows a perspective sectional illustration of an
exemplary embodiment of a housing of a light emitting diode such as
may be used in the optoelectronic arrangement.
DETAILED DESCRIPTION OF THE DRAWINGS
[0050] In the exemplary embodiments and figures, identical and
identically acting constituent parts are in each case provided with
the same reference symbols. The constituent parts illustrated and
also the relative sizes of the constituent parts with respect to
one another are not to be regarded as true to scale. Rather, some
details of the figures have been illustrated with an exaggerated
size in order to afford a better understanding.
[0051] FIG. 1 shows a sectional illustration of a first exemplary
embodiment of a printed circuit board described here. The printed
circuit board 6 has a basic body 4 made of FR4, for example. By way
of example, the printed circuit board 6 is provided by an FR4
printed circuit board coated with copper on both sides. However,
other printed circuit board materials such as FR2, FR3, CEM1, CEM2,
Teflon, aramid or other materials are also conceivable as a basic
body of the printed circuit board.
[0052] In this case, the basic body preferably has a thickness of
between 1.4 and 2.4 mm. The electrical connection locations 3a, 3b
are applied to the basic body 4. They serve for connecting and
making electrical contact with a component. The connection
locations 3a, 3b preferably contain copper. A copper layer 5 may be
applied to the underside of the basic body 4 of the printed circuit
board.
[0053] The printed circuit board 6 furthermore has a perforation,
for example a hole, into which a heat conducting element 2 is
inserted. For mechanical fixing to the basic body 4, the heat
conducting element 2 is, for example, thermally stably adhesively
bonded or soldered on. In this case, the diameter of the heat
conducting element 2 preferably corresponds to the diameter of the
hole. The diameter may preferably be adapted to the area of the
thermal connection part 22 of a component 20 to be mounted onto the
printed circuit board 6 (see FIG. 3). The diameter of the heat
conducting element 2 is between 3 and 5 mm, for example.
[0054] The heat conducting element 2 is preferably provided by a
copper lamina. The heat conducting element 2 is preferably a solid
body comprising copper. As an alternative, however, it is also
possible for the heat conducting element to comprise another
material exhibiting good thermal conduction.
[0055] In the present exemplary embodiment, a thermally conductive
and electrically insulating layer 1 is applied to the heat
conducting element 2. The layer 1 comprises diamondlike carbon
(DLC) and is applied by means of a plasma coating method. The
thickness of the layer 1 is preferably approximately 2 .mu.m. It
has an electrical resistivity of approximately 10.sup.10 .OMEGA.m
and a thermal conductivity of 500 to 700 W/mK. The layer
considerably improves the thermal coupling of an optoelectronic
component 20 connected to the layer 1 and of the heat conducting
element 2. There is a fixed mechanical connection between the layer
1 and the heat conducting element 2. With the aid of the layer, it
is possible to reduce the thermal resistance for the section from
the thermal connection part 22 of the optoelectronic component 20
to the underside of the printed circuit board, with the use of a
heat conducting element made of copper, to approximately 0.1 K/W.
This is approximately 1/10 of the thermal resistance without a
thermally conductive and electrically insulating layer 1. Only the
heat conducting element 2 then makes an appreciable contribution to
the thermal resistance of the arrangement.
[0056] FIG. 2 shows a further exemplary embodiment of the printed
circuit board described. In this case, an underside coating 7 is
applied on the underside of the printed circuit board 6. The
underside coating 7 preferably comprises diamondlike carbon. Its
thickness is preferably between 1 .mu.m and 3 .mu.m. The underside
coating 7 advantageously covers the underside of the printed
circuit board 6 as completely as possible. As a result, the
underside coating 7 also preferably completely covers the underside
of the heat conducting element 2. On the one hand, the underside
coating 7 serves for areally distributing the heat passing through
the heat conducting element 2 on the underside of the printed
circuit board 6. On the other hand, the underside coating 7
improves the thermal coupling between printed circuit board 6 and a
heat sink to which the printed circuit board 6 may be applied for
example by its underside. In this case, as shown in FIG. 2, the
underside coating 7 also covers the copper layer 5 as completely as
possible.
[0057] It is also possible, moreover, for only the heat conducting
element 2 to have an underside coating 7 at its underside and for
the remaining underside of the printed circuit board 6 to be
uncoated. In this way, heat can be emitted directly to a heat sink
by the heat conducting element 2 without the heat previously being
distributed areally on the underside 7 of the printed circuit
board.
[0058] FIG. 3 shows an exemplary embodiment of the optoelectronic
arrangement described. An optoelectronic arrangement with a light
emitting diode 20 is shown here by way of example. The electrical
connection parts 23a, 23b of the light emitting diode are for
example soldered onto the connection locations 3a, 3b of the
printed circuit board 6. The thermal connection part 22 of the
light emitting diode is soldered or thermally stably adhesively
bonded onto the thermally conductive and electrically insulating
layer 1. As an alternative, the layer 1 is formed by a coating of
the thermal connection part 22 of the light emitting diode. The
layer 1 is then adhesively bonded or soldered onto the heat
conducting element 2, by way of example. Moreover, both the light
emitting diode 20 at its thermal connection part 22 and the heat
conducting element 2 may have a thermally conductive and
electrically insulating layer 1.
[0059] The light emitting diode 20 is preferably a high-power light
emitting diode having a power consumption of at least 1 W. In this
case, the light emitting diode 20 may be suitable, for example, for
the emission of white light.
[0060] FIG. 4 shows a perspective sectional illustration of a
housing of a light emitting diode 20 described here. The housing
has a basic body 26, for example, which may comprise a plastic
moulding composition and may be produced for example by means of an
injection moulding or transfer moulding method. The moulding
composition contains, for example, a plastic material based on an
epoxy resin or an acrylic resin. The thermal connection part and
also the electrical connection parts 23a, 23b are embedded into the
basic body 26. The chip mounting region 25, on which a light
emitting diode chip can be mounted, is situated on the thermal
connection part 22.
[0061] The light emitting diode chip may be, for example, a light
emitting diode chip of thin-film design in the case of which the
growth substrate is removed and the heat generated during operation
of the chip is emitted to the thermal connection part 22 via a
carrier (not shown but, as is well known, this refers to a suitable
layer bonded to the side of the chip facing away from the growth
substrate after the latter has been removed) exhibiting
particularly good thermal conduction. A thin-film light emitting
diode chip may be distinguished in particular by the following
characteristic features: [0062] a reflective layer is applied or
formed at a first main area of a radiation-generating epitaxial
layer sequence that faces toward a carrier element, said reflective
layer reflecting at least a part of the electromagnetic radiation
generated in the epitaxial layer sequence back into the latter;
[0063] the epitaxial layer sequence has a thickness in the region
of 20 .mu.m or less, in particular in the region of 10 .mu.m; and
[0064] the epitaxial layer sequence contains at least one
semiconductor layer with at least one area having a disordering
structure that ideally leads to an approximately ergodic
distribution of the light in the epitaxial layer sequence, i.e. it
has an as far as possible ergodically stochastic scattering
behaviour.
[0065] A basic principle of a thin-film light emitting diode chip
is described for example in I. Schnitzer et al., Appl. Phys. Lett.
63 (16), Oct. 18, 1993, 2174-2176, the disclosure content of which
in this respect is hereby incorporated by reference.
[0066] A thin-film light emitting diode chip is to a good
approximation a Lambert surface radiator and is, therefore,
particularly well suited to application in a headlight.
[0067] The thermal connection part 22 is electrically
contact-connected for example with the electrical connection part
23b. The thermal connection part 22 preferably contains a material
exhibiting good electrical and thermal conduction, such as copper
for example. The connection part 22 preferably comprises
copper.
[0068] The underside of the thermal connection location 22 may be
coated with a layer 21 made of diamondlike carbon. For this
purpose, the underside of the thermal connection part 22 preferably
projects slightly beyond the underside 24 of the basic body 26. The
layer 21 may be either an additional coating with diamondlike
carbon or the layer 1. Owing to its high electrical resistance, the
layer 21 also contributes to the electrical decoupling of the light
emitting diode in addition to its very good heat conducting
property.
[0069] The invention is not restricted by the description on the
basis of the exemplary embodiments. Rather, the invention comprises
any new feature and also any combination of features, in particular
any combination of features in the patent claims, even if this
feature or this combination itself is not explicitly specified in
the patent claims or exemplary embodiments.
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